After decades of devotion, the British teenager is falling out of love with the television. For many, the old TV set is no longer the first thing they turn to after a day at school. Sadly for teachers, it's not always homework that kids are turning to as a substitute, but rather a group of fast-growing websites that let them watch - and communicate with - each other.

In the past 12 months, "social networking" has gone from being the next big thing to the thing itself. Last month, MySpace, the site that famously propelled the Arctic Monkeys to pop stardom, overtook the BBC website in terms of visitor numbers. Along with competing sites Bebo and Facebook, MySpace has formed one of the fastest growing sectors on the internet. Latest data from the internet traffic monitor Hitwise reports that visits to MySpace, the market leader, have grown sixfold year on year, while those to rivals Spaces.MSN.com are up 11-fold and to Bebo.com an amazing 61 times more.

To their users, social networking sites fill a number of functions: part diary, part shareable contacts book, part social club. For a generation of teenagers, they are increasingly becoming as important as ownership of a mobile phone. The fastest growing is Bebo.com, which, like its US counterpart Facebook.com, bases its membership around lists of schools and colleges, a kind of Friends Reunited for people who are still there. And teenagers are taking to Bebo quicker than they can pop a can of paprika-flavoured Pringles; there are 4 million in the UK alone.

Each Bebo user - or Beboer - is given their own mini-homepage that they use to represent themselves. Some list favourite bands or movies or display their football allegiances. Others generate delicate illustrations comprised entirely of ASCII characters, while more set polls and arrange topical debates or simply wallow in the latest school gossip.

Bebo is based in California but the company's founder, Michael Birch, was raised in the Hertfordshire village of Cuffley, before moving to London to study physics at Imperial College. There he met his wife Xochi, a native of California. The pair hatched two websites: Birthdayalarm.com and Ringo.com, a virtual address book. The latter they sold to Tickle.com, an online dating service, for a significant, but undisclosed, sum. The pair now live in the suburbs of San Francisco with their two children.

Purely personal

"Email is very limited in what you can do with it," explains Birch. "With Bebo, everything you get is purely personal mail. When you get a mail you can click on their name and learn so much about the person who sent it." So much so that the standard email exchange feels naked by comparison.

So what do Beboers do that is so compelling? The simple answer is nothing radically new. Beboers send email, exchange voice messages, share photos and, naturally for teenagers, trade insults. And as of last month, members can also make voice calls over the Bebo network thanks to a partnership deal with internet phone company Skype. "It's pulling all the different media together," says Birch. "It used to be phone, then email, then SMS. But now Bebo does all of these things but with photos, quizzes, drawings and blogs thrown in."

The big difference is that they are using the individual tools - email, chat, voice calls, photo-sharing - together, as if they were all part of a single tool. Together they form a kind of interactive, multimedia channel for the whole school. No need for lots of multiple downloads, no need for multiple accounts and passwords for lots of different services. All your means of communication are available on Bebo and so are all of your mates.

But it's one thing to pull the kids in, another to keep them happy. According to Heather Hopkins, director of research for Hitwise, the "net community and chat" sector - to which Bebo belongs - can be as fickle as teenage love. "At least 40% of this year's top 10 will be nowhere this time next year," she says. This is because the launch of a new social networking site is like the opening of the latest uptown bar. They are events in themselves, meaning sites experience huge swells in traffic before receding as certainly as the onset of the next day's hangover.

Bebo.com is, indeed, on its second bout. More than half its users registered when it was essentially a photo-sharing site back in January last year, but traffic stalled until, last June, it relaunched, focusing on colleges and high schools. It has not looked back.

Marketing blizzard

In its first year, Bebo - thanks mostly to a blizzard of email marketing campaigns (the site spent nothing on conventional advertising) - has attracted 21.4 million registered users worldwide, 4 million of whom live in the UK. And while only about a quarter of registrations become highly active, that still equates to more than 700m page impressions every month.

However, the backlash to social networking sites has begun. Two years ago, prominent blogger Russell Beattie famously chose to opt out of LinkedIn (linkedin.com), an early precursor to Bebo, saying he was overwhelmed with personal data about people he didn't know nor particularly cared to know. But what many affluent adopters and super-connected bloggers fail to realise is that a younger generation, native to the internet, would feel quite different. To them, social networking technology is fast becoming a default rather than an option.

And this is, perhaps, what makes Bebo so exciting. Although, hypothetically at least, it is possible for Beboers to contact any one of its 20 million members, most use the network not to make thousands of new friends, but "to keep tabs on people you already know," says David Mosby ("Moz" to fellow Beboers). Like many 17-year-olds, Moz has grown up on the internet. He got into Bebo by accident, being sent an email invitation from a friend a few months ago. Now he's on it every night, talking to friends from school and new ones from overseas.

Bebo caught on at his school, Oakbank in Keithley, at the start of this academic year and spread like a benign, although extremely virulent, infection. So quickly, in fact, that within a matter of days it had been banned from the school servers. It didn't matter. Bebo continued to grow after school because many children have long enjoyed the internet at home. And Oakbank school is lucky: teachers at least knew about the students' double lives, although the site has been placed on ban lists by a number of local education authorities, which mistake the site for an ordinary chatroom.

Bebo also represents something beyond any school's control. Several teachers contacted by Technology Guardian were alarmed that so much of their pupils' personal lives were paraded in such a way without their knowledge. At the heart of social networking is an exchange of personal information. And many users are happy to casually reveal intimate details of their personal lives, which concern many adults and internet safety experts.

Rachel O'Connell advises the government on internet safety. She recently chaired a conference in London looking at the inherent dangers of social networking. "The etiquette on these sites is to post accurate information, and to share photographs, which flies in the face of internet safety advice," she says. "In this particular social networking environment, the premise is affording people the opportunity to network with friends and friends of friends, much as you might do in a school. That's a worry because people detail which school they attend, their age, and provide photos."

Enhancing communication

Bebo says its method of communication is safer than regular email, in a very practical sense. It argues that because each user is required to give so much personal information, it is much more difficult to be abused. "Bebo is all about enhancing Beboers' real life, not replacing it," says Jim. His official title is "the deal guy". He cut his teeth at Friendster, an early example of social networking that blazed for a few years before falling off to nowhere. "We have had a few isolated instances of abuse," he admits, "but these were rectified quickly." The fact that abuse was reported swiftly demonstrates, so far, that it has the ability to self-police.

Bebo may fall the same way as Friendster, but the most net-savvy nation suggests it may be here for good. In the tower blocks of South Korea, the kind of intimacy played out by the Beboers is already being witnessed on a national scale. Although few use names such as social networking, South Korea is hooked into Cyworld.

It is more sophisticated than western equivalents - Cyworld's integration with the mobile phone makes Bebo look primitive - but it carries the same show-and-tell culture. It is a cartoony, super-flat mirror universe but most of Korea's social activity already revolves around it. And according to Jee Hyun Oh, a devotee of Cyworld, "social death awaits" those who fail to link up. Teenagers and parents, take note.

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